Emacs has several packages for dealing with parentheses. Emacs comes with ways to highlight the matching parenthesis when you're on one; try show-paren-mode. One of the newer add-on packages is Nikolaj Schumacher's highlight-parentheses mode, which
shows the parentheses that enclose the current cursor position. I tried modifying it to highlight the containing expressions instead of only their parentheses:

Unfortunately, as you can see, it's a mess. I tried better colors (white, gray, etc.) but I just couldn't make it usable. So I gave up on highlighting the regions and went back to highlighting just the parentheses. It's a bit better:

It bolds the parentheses and also the first s-expression inside the opening parenthesis. It doesn't understand when the parentheses begin a form (instead of all the other uses of parentheses), so it sometimes highlights the first s-expression even when it's not special in any way. Despite this wart, I like this form of highlighting so far.

Update: [2007-05-29] However, there is one more thing I wanted. I de-emphasize parentheses by using a lighter color for them; I want the enclosing parentheses to be bold and black. However I want the enclosing first s-expressions to be bold, but not necessarily black. Note in the above example the keywords are normally blue, but when enclosing the current point they are black. I fixed this by adding separate highlighting for the enclosing parentheses and the first s-expression:

My version is pretty messy and doesn't work reliably, so I didn't put it up. A few days after Anonymous asked, Nikolaj put up a new version with optional background highlighting and bolding. It doesn't highlight the first sexp; I might try patching it to support that.